Silicone rubber compositions and long-term-stress-resistant silicone elastomers obtained therefrom

Abstract

The present invention relates to silicone rubber compositions and long-term-stress-resistant silicone elastomers obtained therefrom, which have excellent resistance to long-term dynamic mechanical stresses, and to their use.

1. A peroxidically curable crosslinkable silicone rubber composition comprising
 (A) 100 parts by weight of at least one polydiorganosiloxane comprising organosiloxy units having Si—C-bonded, aliphatically unsaturated groups, polydiorganosiloxane (A) having
 (a) a mean degree of polymerization of from 3000 to 10,000, 
 (b) from 0.2 to 20 mol % of organosiloxy units comprising aliphatically unsaturated groups, and 
 (c) a low-segregation distribution of the organosiloxy units comprising aliphatically unsaturated groups, with the proviso that the block number R is ≧180·X a ·(1−X a ), where X a  is the mole fraction of these organosiloxy units 
 
 (B) 1-90 parts by weight of at least one reinforcing filler which is present as a finely divided, inorganic solid having a specific surface area of at least 30 m 2 /g, 
 (C) 0.1-20 pans by weight of at least one crosslinker which is an organic peroxide, 
 (D) 0-10 parts by weight of a polydiorganosiloxane which is terminated by vinyldiorganosiloxy groups at both ends, whose non-terminal units are free of aliphatically unsaturated groups, and which has a mean degree of polymerization of from 3000 to 10,000, 
 (E) 0-200 parts by weight of one or more further constituents selected from the group consisting of nonreinforcing fillers, talc, quartz flour, inhibitors, plasticizers, pigments, stabilizers, flame-retardant additives, bonding agents, mold release agents, hollow microspheres and mixtures thereof, wherein the organosiloxy groups comprising aliphatically unsaturated groups are randomly distributed in the polydiorganosiloxane (A). 
 
     
     
       2. The crosslinkable silicone rubber composition of  claim 1 , wherein the polydiorganosiloxane (A) contains a proportion of from 0.4 to 10 mol % of organosiloxy units having aliphatically unsaturated groups. 
     
     
       3. The crosslinkable silicone rubber composition of  claim 2 , wherein the filler (B) is a surface-treated silica comprising from 0.01 to 2% by weight of Si-bonded, aliphatically unsaturated groups. 
     
     
       4. The crosslinkable silicone rubber composition of  claim 1 , wherein the filler (B) has been surface-treated. 
     
     
       5. The crosslinkable silicone rubber composition of  claim 1 , wherein the filler (B) is a surface-treated silica comprising from 0.01 to 2% by weight of Si-bonded, aliphatically unsaturated groups. 
     
     
       6. The crosslinkable silicone rubber composition of  claim 1 , wherein a crosslinker (C1) is present in an amount of from 0.1 to 5.0% by weight and is an organic peroxide or a mixture of organic peroxides. 
     
     
       7. A silicone elastomer obtained by crosslinking the silicone rubber composition of  claim 1 . 
     
     
       8. A keyboard or keyboard cover comprising the elastomer of  claim 7 . 
     
     
       9. A process for producing a silicone elastomer of  claim 1 , comprising crosslinking the silicone rubber composition at elevated temperature, and at atmospheric pressure or higher pressure. 
     
     
       10. The process for producing silicone elastomers of  claim 9 , wherein the silicone elastomer is heat treated at elevated temperature after crosslinking. 
     
     
       11. The composition of  claim 1 , wherein the organo groups of the polydiorganosiloxane (A) are selected from the group consisting of methyl groups and vinyl groups. 
     
     
       12. The composition of  claim 1 , wherein the only crosslinker contained in the composition is an organic free radical initiator. 
     
     
       13. A peroxidically curable crosslinkable silicone rubber composition comprising
 (A) 100 parts by weight of at least one polydiorganosiloxane comprising organosiloxy units having Si—C-bonded, aliphatically unsaturated groups, polydiorganosiloxane (A) having
 (a) a mean degree of polymerization of from 3000 to 10,000, 
 (b) from 0.2 to 20 mol % of organosiloxy units comprising aliphatically unsaturated groups, and 
 (c) a low-segregation distribution of the organosiloxy units comprising aliphatically unsaturated groups, with the proviso that the block number R is ≧180·X a ·(1−X a ), where X a  is the mole fraction of these organosiloxy units 
 
 (B) 1-90 parts by weight of at least one reinforcing filler which is present as a finely divided, inorganic solid having a specific surface area of at least 30 m 2 /g, 
 (C) 0.1-20 parts by weight of at least one crosslinker which is an organic peroxide, 
 (D) 0-10 parts by weight of a polydiorganosiloxane which is terminated by vinyldiorganosiloxy groups at both ends, whose non-terminal units are free of aliphatically unsaturated groups, and which has a mean degree of polymerization of from 3000 to 10,000, 
 (E) 0-200 parts by weight of one or more further constituents selected from the group consisting of nonreinforcing fillers, talc, quartz flour, inhibitors, plasticizers, pigments, stabilizers, flame-retardant additives, bonding agents, mold release agents, hollow microspheres and mixtures thereof, wherein the polydiorganosiloxane (A) is a vinyldimethylsiloxy-terminated copolymer of siloxy groups consisting of both dimethylsiloxy and methylvinyldiloxy groups. 
 
     
     
       14. The composition of  claim 13 , wherein polydiorganosiloxane (A) contains from 0.4 to 10 mol % of organosiloxy units comprising aliphatically unsaturated groups. 
     
     
       15. The composition of  claim 13 , wherein the organo groups of the polydiorganosiloxane (A) are selected from the group consisting of aliphatically unsaturated hydrocarbon radicals and unsubstituted C 1-20  hydrocarbon radicals free of aliphatic unsaturation.